1. Field of the Invention
This invention relates to resin compositions suitable for toner. More particularly, it relates to resin compositions suitable as binder for electrophotographic toner.
2. Description of the Prior Art
In electrophotography (xerography), for fixing electrostatic latent images visualized with use of a developing toner, there have been widely used methods using fixing means of contact heating, such as those with a heated roller and those via a film or a between a heater and paper or the like (for example, JPN Patent Lay-open No. 70688/1992 and No. 12558/1992. In these methods, it is desired that the minimum temperature for fixing (hereinafter referred to as MF) is low (low temperature fixing properties) and the temperature causing offset to the heated roller (hereinafter referred to as HO) is high (anti-hot offset properties). Thermal shelf stability is also desired so as not to cause coagulation (or agglomeration) and reduction of flowability under heat evolved from fixers within electrophotographic machines.
In order to meet these requirements, there have been heretofore proposed various techniques using toner binders having wide range of molecular weight distribution from lower molecular weight to higher molecular weight and having a glass transition temperature (hereinafter referred to as Tg) (for example, JPN Patent Publications No. 20411/1985 and JPN Patent Lay-open No. 21555/1986), and those using toners mainly composed of heat reaction products of non-crystallizable polyester resins with vinyl copolymer resins (for instance JPN Patent Lay-open No. 277074/1990).
In these techniques, there are drawbacks, that the formers cannot sufficiently answer to fixing properties at lower temperature required in racent high speed facsimile or copy machines, or to higher thermal shelf stability desired accompanied with miniaturization of printers; and that the latters result in poor dispersibility of colorants and charge controllers, insufficient frictional charge amount, liablity of vinyl resin bleeding out of polyester resin matrix to toner surface, and difficulty in viscosity reduction.